And I just found out about something called "spiteful mutations", which would seem to be the mechanism I was searching for.
Take away selection pressure, and these spiteful mutations build up in a population, or in many populations, of a "privileged" species. These mutants have a socially detrimental effect on the other people (of whatever species) around them, and their society eventually falls apart, causing a dieback; it keeps cycling until the species goes extinct. (Or evolves its physical form in a way that makes it appear to have gone extinct.) And yeah, I can see each dieback resulting in a pulse of technological progress, and a concurrent dependency upon that technology, which leads to prosperity, mutations, and dieback ...
And I just found out about something called "spiteful mutations", which would seem to be the mechanism I was searching for.
Take away selection pressure, and these spiteful mutations build up in a population, or in many populations, of a "privileged" species. These mutants have a socially detrimental effect on the other people (of whatever species) around them, and their society eventually falls apart, causing a dieback; it keeps cycling until the species goes extinct. (Or evolves its physical form in a way that makes it appear to have gone extinct.) And yeah, I can see each dieback resulting in a pulse of technological progress, and a concurrent dependency upon that technology, which leads to prosperity, mutations, and dieback ...